7/14/2010
Routine Ultrasound Equipment Tests for
Quality Assurance
James A. Zagzebski, Ph.D.
Ph.D.
Nick Rupert, M.S.
Ryan DeWall
DeWall,, M.S.
Tomy Varghese, Ph.D.
Dept. of Medical Physics
University of Wisconsin, Madison, WI, USA
Contents
• Elements of a Routine Test Program
• What system components are considered
most important in routine testing?
Concentrate on transducers!
• Steps to carry out tests on a regular basis
• Activity of Ultrasound Lab Accreditation
Groups
• Basic QA methods
Phantoms and tests
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Routine QA Program
• Guidelines available from US facility
accreditation bodies (ACR; AIUM)
• Emphasis is given to safety, cleanliness, and
very basic performance tests.
• Issues related to image performance, such as
spatial resolution, are not included (except
ACR breast).
• Traditional “parameters” such as distance
measurements are believed by many to be
unnecessary. Includedi n some protocols, but
only briefly.
Routine QA (ACR General US Program)
• System sensitivity and/or penetration capability
1999: Do for 2 probes (?)
• Image Uniformity
Look for element dropout
• Photography and other hard copy recording
2010: workstation monitor display
• Low contrast object detectability
• Assurance of electrical and mechanical safety
and sterility
• Verify measurement accuracy during program
initiation
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American College of Radiology Requirements:
General Sonography
• ACR physics committee developing this standard based it
on measurements using a phantom.
A phantom was selected (fall,1998) but turned out to be much
more costly than originally promised.
Physics Committee chose to leave the choice of phantoms to the
user
ACR staff published the following:
• “Using a phantom will be helpful in responding to questions
about low contrast detectability …. However, the use of a
phantom is optional at this time. Questions relating to
characteristics associated with system sensitivity and image
uniformity may be answered without the use of a phantom or
test object.”
American Institute of Ultrasound in Medicine:
General US QC
• 2008
• Originally called “QA in the
Clinic”
Sonographers and clinicians
helped draft
• Outlines what to do
Sonographers
Physicists/engineers
• Limited information on
methodology
Requires a phantom
Phantom left to users
• See www.aium.org
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American Institute of Ultrasound in Medicine:
General US QC
American Institute of Ultrasound in Medicine:
General Sonography (physicist, engineer)
• Transducer Uniformity
Phantom
Electronic probe tester
• Sensitivity, Maximum depth of visualization into a
•
•
phantom
Distance measurement accuracy
Target detection and imaging
Focal targets such as simulated cysts or low contrast objects
Choice of phantoms left to users
• Image display fidelity
• Cables OK, air filters clean, mechanical and electrical
•
inspection
Minimum frequency
Annual for physicists/engineer tests
Program includes daily, weekly checks by sonographers
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Currently used materials:
Water-based gels
Water Advantages:
Speed of sound = 1540
m/s
Attenuation proportional
to frequency
Backscatter
Disadvantages:
Subject to desiccation
Must be kept in containers
Requires scanning
window
Currently used TM materials:
• Solid, non
non--water
water--based
materials (urethane)
• Advantages
Advantages::
Not subject to desiccation
No need for scanning
window
Produce tissue-like
backscatter
Disadvantages:
C= 1430-1450 m/s
Attenuation not proportional
to frequency (~f1.6)
Surface easily damaged if
not cleaned regularly to
remove gels
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Maximum Depth of Visualization
• Considered by many as a good
•
•
•
•
overall check of the integrity of
the system
FOV at 18 cm (or set to match
the phantom)
Output power (MI) at max
Transmit focus at deepest
settings
Gains, TGC for visualization to
the maximum distance
possible
Maximum Depth of Visualization
How far can you see the speckle pattern in the material?
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Objective Maximum Depth of Visualization
• Gibson, Dudley, Griffith, “A computerized Quality Control System for
B-mode Ultrasound,” Ultrasound Med Biol 27:1697
27:1697--1711, 2001.
• Shi, AlAl-Sadah
Sadah,, Mackie, Zagzebski, Signal to Noise Ratio Estimates
•
•
•
on Ultrasound Depth of Penetration (abstract only), Medical Physics
30:
30: 11367, 2003.
Gorny,, Tradup,
Gorny
Tradup, Bernatz,
Bernatz, Stekel,
Stekel, and Hangiandreou,
Hangiandreou, “Evaluation of
an Automated Depth of Penetration Measurement ofr the Purpose of
Ultrasonic Scanner Comparison”, (abstract only), J. Ultrasound Med
MPV’
23: S76, 2004.
Compute mean pixel value vs depth for phantom (signal) and for
noise only (noise)
(noise)
Depth where signal/noise = 1.5 =DOP
SNR’-DOP tracks well Observer-DOP
Observers-DOP & SNR-DOP comparision (ATL C5-2)
16
15
14
Depth (cm)
13
12
11
10
9
Observer's DOP
DOP using SNR'= 1.5
8
7
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Mechanical Index MI
(Al-Sadah, UW-Madison)
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Routine QA: Image Uniformity
Considered to be
the most imporimportant and useful
test!
Ideally:
No evidence of
element dropout
No vertical
‘shadows’
No loss of
sensitivity near
edges
Uniformity
Turn off spatial
compounding,
speckle reduction
Use 1 tx focus
Search for
“shadows”
emanating from
transducer
Common in new
and old probes!
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Difficulties with Uniformity
• Coupling to a flat surface phantom scanning window with
curvilinear transducers
Difficulties with Uniformity
• Coupling to a flat surface phantom scanning window with
curvilinear transducers
• Solution 1: rock transducer from side to side
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Difficulties with Uniformity
• Coupling to a flat surface phantom scanning window with
curvilinear transducers
• Solutside to side
Difficulties with Uniformity
• Coupling to a flat surface phantom scanning window with
curvilinear transducers
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Difficulties with Uniformity
• Coupling to a flat surface phantom scanning window with
curvilinear transducers
• Solution 2: Use a liquid TM material
Difficulties with Uniformity
• Coupling to a flat surface with curvilinear transducers
Sensitivity
1
Volts p-p
0.8
0.6
0.4
0.2
0
1
11
21
31
41
51
61
71
81
91
101
111
121
Elements
Electronic Probe test
• Solution 2: Use a liquid TM material (pseudo liquid TM
slurry; Madsen et al.)
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Difficulties with Uniformity
• Coupling to a flat surface phantom scanning window with
curvilinear transducers
• Solution 3: Use a phantom having concave windows
(Goodsitt et al)
Difficulties with Uniformity
• Visualizing 11-2 element dropouts
• Use persistence; translate transducer.
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Difficulties with Uniformity
• Visualizing 11-2 element dropouts
• Use persistence; translate transducer.
Difficulties with Uniformity
• Visualizing 11-2 element dropouts
• Record Image loops while translating the transducer;
• Compress a 100 frame loop into 1 image (averages
speckle)
1 image
Ultrasonix SonixTouch
Enables masking off
individual elements
Elements 95 and 96
masked
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Difficulties with Uniformity
• Visualizing 11-2 element dropouts
• Record Image loops while translating the transducer;
• Compress a 100 frame loop into 1 image (averages
speckle)
Average image
Ultrasonix SonixTouch
Enables masking off
individual elements
Elements 95 and 96
masked
Difficulties with Uniformity
• Visualizing 11-2 element dropouts
• Use persistence; translate transducer
• Use Record Image loops while translating the transducer;
•
compress a 100 frame loop into 1 image (averages
speckle)
Phased array transducer performance
Need electronic probe tester
Transducer test modes on the ultrasound instrument are possible;
manufacturers need to be encouraged to provide these
• Future 22-D probes, probes that do part of the beam
forming within the probe housing
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Gray Scale Photography, Workstation
Fidelity
• Important for monitor on machine
to be set up properly to view all
echo levels available and entire
gray bar pattern.
Set up during acceptance testing
Take steps to avoid the “meat hook”
effect (mark or inscribe contrast and
brightness controls)
• Workstation monitors and/or
hardcopy devices should be
matched to the machine monitor.
AAPM, July, 2010
Check hardcopy, workstation displays.
Are all gray bar transitions visible?
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SMPTE Test Pattern
• Available on most
•
•
•
scanners
0% to 100% gray
bar pattern
Squares for
detecting geometric
distortion
Are all gray
transitions visible?
Distance Measurement Accuracy: Vertical
Actual 2.5
Measure 2.46
error 1.5%
Acceptable
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Distance Measurement Accuracy: Horizontal
Actual 1.0
Measure 1.01
error <1%
Acceptable
Routine QA (ACR General US Program)
• Distance Measurement Accuracy tests as needed
Necessary? (“Scanner is a transducer tied to a computer.”)
May be important for specific uses
• Images reregistered from 3-D data sets
• Workstation measurements
• Radiation seed implants
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ACR Recommended QC for Breast US
Maximum Depth of
visualization
Semiannually
Service eng./physicist
Vertical and horiz
measurement accuracy
Semiannually
Service eng./physicist
Hardcopy Recording
Semiannually
Service eng./physicist
Uniformity
Semiannually
Service eng./physicist
Elec-mechanical condition
Semiannually
Service eng./physicist
Anechoic void perception
Semiannually
Service eng./physicist
Ring down
Semiannually
Service eng./physicist
Lateral Resolution
Semiannually
Service eng./physicist
QC Checklist
Semiannually
Service eng./physicist
Adherence to infection
control procedures
After each biopsy
Sonographer
Clean transducers
After each biopsy
Sonographer
Vertical and horiz
measurement accuracy
Quarterly
Sonographer
Grey-scale photography
Quarterly
Sonographer
Dead Zone?
No suitable targets for
dead zone testing,
even in phantoms
that advertise
deadzone tragets
tragets!!
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Anechoic Sphere Imaging, a better choice
Anechoic Sphere Imaging
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Image of a phantom is useful for qualitative
comparisons!
Conventional
Spatial Compounding
Images obtained during routine Breast QC testing, 3/2010
Image of a phantom is useful!
Conventional
Spatial Compounding
Images obtained 1 month later, after a software change;
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Routine QA: Cleanliness, safety
Transducer Inspection
Delaminations
Frayed cables
Proper cleaning
Console
Air filters
Viewing monitor, keyboard clean
Lights, indicators
Wheels, wheel locks
Proper cleaning
Summary
• Setting up, maintaining an equipment QA program is
•
•
•
straight forward
The ACR listed procedures are a useful, basic QA
program
Directed by physicist or lab personnel
Integrated effort including lab and technical staff
Requires a Phantom
Closely correlates with AIUM list of factors to test
Transducer uniformity is a frequent fault in today’s
scanning machines
Computational methods can be developed for
objective tests
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References
• Goodsitt et al, “Real“Real-time BB-mode ultrasound quality control test
procedures”, Medical Physics 1998; 25:138525:1385-1406.
• J Zagzebski, “US quality assurance with phantoms.” In Categorical
•
•
•
Course in Diagnostic Radiology Physics: CT and US CrossCross-Sectional
Imaging, Edited by L. Goldman and B. Fowlkes, 2000, Oak Brook, IL:
Radiological Society of North America, pp. 159159-170.
J Zagzebski and J Kofler, “Ultrasound Equipment Quality Assurance,”
in Quality Management in the Imaging Sciences, ed. By J Papp, 2002,
St. Louis, Mosby, pp. 207207-215.
QA Manual for Gray Scale Ultrasound Scanners, 1995, American
Institute of Ultrasound in Medicine, Laurel, MA.
D Groth et al, “Cathode ray tube quality control and acceptance
program: initial results for clinical PACS displays, Radiographics
2001, 21: 719.
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